Molecular sieves are a commercially important class of crystalline materials. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species. Molecular sieves such as zeolites have been used extensively to catalyze a number of chemical reactions in refinery and petrochemical reactions, and catalysis, adsorption, separation, and chromatography.
SSZ-31 is a high-silica molecular sieve material with a large one-dimensional pore system. The pore apertures are elliptical with a dimension of approximately 8.6×5.7 Å. The structure of SSZ-31 is highly faulted and can be described as an intergrowth of four different but structurally related polymorphs.
The framework structure of SSZ-31 has been assigned the three letter code *STO by the Structure Commission of the International Zeolite Association.
The composition and characterizing powder X-ray diffraction pattern of SSZ-31 are disclosed in U.S. Pat. No. 5,106,801, which also describes the synthesis of the borosilicate form of the zeolite in the presence of a structure directing agent selected from one or more of N,N,N-trimethylammonium-8-tricyclo[5.2.1.0]decane, 4-trimethylammonium-2,2,6,6-tetramethylpiperidine, N,N-dimethyl-3-azonium bicyclo[3.2.2]nonane, N,N,N-trimethylammonium-2-bicyclo[3.2.1]octane, N,N-dimethyl-6-azonium-1,3,3-trimethylbicyclo[3.2.1]octane, and 1,1,3,5,5-pentamethyl azonium cycloheptane. An all-silica form of SSZ-31 was also synthesized using N,N,N-trimethylammonium-8-tricyclo[5.2.1.0]decane as a structure directing agent.
Due to the very large pore diameter of SSZ-31, aluminum-containing forms of SSZ-31 are of interest for shape-selective catalysis, such as alkylation of relatively bulky aromatic compounds. Aluminosilicate SSZ-31 may be prepared from borosilicate SSZ-31 by heteroatom lattice substitution techniques such as described in U.S. Pat. Nos. 6,468,501 and 6,790,433.
U.S. Pat. No. 6,471,940 discloses the direct synthesis of aluminosilicate SSZ-31 by a dry gel conversion method using a structure directing agent selected from one of more of N,N′-bis-triethyl-1,6-hexanediyl-diammonium dihydroxide, N,N′-bis-triethyl-1,7-heptanediyl-diammonium dihydroxide, N,N′-bis-triethyl-1,8-octanediyl-diammonium dihydroxide, N,N′-bis-triethyl-1,9-nonanediyl-diammonium dihydroxide, and N,N′-bis-triethyl-1,10-decanediyl-diammonium dihydroxide.
According to the present disclosure, it has now been found that 1-cyclohexylmethyl-1-ethylpiperidinium cations are effective as structure directing agent in the direct synthesis of all-silica and aluminosilicate forms of zeolite SSZ-31.